Traditional gait analysis considers the foot as a single rigid body with no intrinsic motion. The quantitative data that this approach provides has proven useful in clinical studies and in research aimed at assessing the behavior of the hip, knee and ankle under various conditions, but it fails to provide meaningful information regarding the behavior of the foot itself. Aberrant motion and flexible deformities of the foot are common clinical manifestations of cerebral palsy and stroke, and better tools are needed for diagnosing their cause and assessing treatment. Over the last several years investigators have proposed methods for measuring the motions of different regions of the foot as a means of providing a more quantitative assessment of foot function in health and disease. These methods consider the foot as a system of segments, whereby the tibia, hindfoot, and forefoot are treated as separate rigid bodies that move relative to each other. The technique could prove to be a valuable clinical tool, but its utility has not yet been objectively evaluated. The aim of this work is to determine the error associated with assuming that certain segments of the foot are rigid during walking, an inherent feature of multi-segment models of the foot, and to determine the ability of the multi-segment approach to detect and correctly identify common neuromuscular pathologies. Satisfying these aims will provide researchers and clinicians with objective and quantitative information concerning the error, or lack there-of, inherent in the multi-segment approach. This information will in turn be instrumental in identifying models that are appropriate for diagnoses and assessment of various lower extremity deficiencies. [unreadable] [unreadable] [unreadable] [unreadable]